HYDROGEN. 51 



in the upper part of the mine, on account of its 

 lightness, but does not mix there with atmospheric 

 air, unless some agitation takes place. The miners 

 frequently set fire to it with a candle, laying, at 

 the same time on their faces, to escape the violence 

 of the shock. An easier and safer method of 

 clearing the mine is, by leading a long tube 

 through the shaft of it to the ash-pit of a furnace ; 

 by this means the gas will be conducted to feed 

 the fire. 



Hydrogen gas, though itself inflammable, extin- 

 guishes burning bodies, and is incapable of main- 

 taining combustion. Bring an inverted jar filled 

 with hydrogen gas over the flame of a candle, and 

 depress the jar, so that the lighted wick may be 

 wholly surrounded by the gas ; the candle will be 

 immediately extinguished. 



Hydrogen gas is only inflammable when in con- 

 tact with atmospheric air or oxygen gas. Fill a 

 small phial with hydrogen gas, and take it from 

 the pneumatic trough, placing the thumb on the 

 mouth thereof, to prevent the gas from escaping ; 

 if a lighted taper be applied to the mouth of the 

 phial, the gas will take fire, and burn with a lam- 

 bent flame. The gas will only burn where it is in 

 contact with the atmospheric air ; the flame will 

 descend gradually, till all the gas is consumed. 



If the hydrogen gas be pure, the flame will be of 

 a blue colour ; but if the gas holds any substance 

 in solution, which is generally the case, the flame 

 is tinged. of different colours, according to the sub- 

 stance. It is usually reddish, because the gas 

 holds in solution a little charcoal. 



On this principle is constructed the philosophical 

 candle, which cannot be easily blown out. Fill 

 with hydrogen gas a bell glass, furnished with a 



